The calibration of total serum bilirubin assays

Bilirubin assays yield variable results due to the lack of a universal calibrant. The preparation of a bilirubin calibrant is associated with the following problems: (a) only unconjugated bilirubin is available in a 'pure' form and this is of doubtful stability, (b) the test for its purity is arbitrary, (c) the true molar absorptivity of bilirubin is unknown, (d) due to the various specificities of methods, the calibrant has to be in a protein matrix, (e) the matrix alters the properties of bilirubin and (f) there is no definitive bilirubin assay. The use of a lyophilised human-based bilirubin calibrant should permit accurate standardisation of the method of Jendrassik and Grof and that of Hertz.